From Schlaifers Enamel web site - sent in by Pam Timm
I have found that in order to manipulate the "silver glass" or Double Helix brand glass you need to use a reducing flame - meaning low oxygen - in order to get the desired effect. If the flame is oxygen rich the effect will come out muddy. Here is some reading on reducing with lampwork glass:http://envisionsf.blogspot.com/2009/04/silver-glass-101-reducing-silver-glass.html
Here is a video: http://www.youtube.com/watch?v=IWlrkgHzFVc
http://www.youtube.com/watch?v=xtf4DXrHHqg
The following Thompson Leaded colors will give a raku look when reduced with a flame. If you torch fire these enamels from underneath and then finish up with playing the torch over the top surface you will get an iridescence on the surface. These are colors that were tried at the Steve Artz workshop.
425 Flux
478 Emerald
644 Soft White
659 Turquoise
724 Gold
728 Amber
736 Chartreuse
741 Cream
755 Mikado
760 Off White
834 Smoke
839 Dark Olive
942 Gray Green
1066 Garnet
122 Imperial Blue
124 Medium Black
160 Lawn Green
167 Chinese Red
175 Flame Red
200 Aquamarine
234 Evergreen
241 Larkspur
290 Blue
320 Nude
334 Ivory
387 Midnight Blue